CEO of e-commerce company says shifting retail industry has created new standard that Shopify has embraced

TORONTO—Shopify Inc.’s shares were down about 10% in recent trading Tuesday after Chief Executive Tobi Lutke addressed a report that questioned the e-commerce platform’s growth rate as “unsubstantiated” during the company’s third-quarter results.

Mr. Lutke addressed a report by short seller Citron Research, well-known among the investor community for targeting companies it believes are overvalued, which criticized Shopify’s business model in a report earlier this month. Shopify’s technology sets up websites, payments and shipping...